Natural gas flows from municipal gas mains to customer locations. At a customer location, gas is routed through smaller pipes into a gas meter. Pipes then carry the gas into a customer residence or business where the gas is ultimately used by appliances or other gas-consuming devices. While gas mains are susceptible to rupture from the violent vibrations caused by earthquakes, the smaller pipes leading into a residence or business are often at higher risk of rupture. In the aftermath of an earthquake, the damage resulting from fires caused by gas pipe rupture can oftentimes exceed the damage resulting from shaking caused by the earthquake.
There are numerous prior art proposals for gas shut-off valves which are designed to respond to earthquakes. Such proposals typically cause false shut-offs in response to non-earthquake vibrations. Furthermore, the prior art shut-off systems proceed to shut-off the gas flow regardless of whether there is a rupture in the gas line. This can result in repeated loss of gas service. As a result, these prior art systems are rarely implemented on a wide scale.
Thus there is the need for a relatively simple, cost-effective system, which can reliably detect the rupture of natural gas pipelines due to earthquake vibration and, in turn, shut-off gas supply only when warranted.